The present invention relates to plunger-operated electrical switches, and particularly to a switch operated by a roller plunger and including a magnetically actuated contact.
Switch assemblies in which a moving body contacts a plunger equipped with a roller, and in which depression of the plunger opens or closes the switch contacts, are well known. One application for such switches is in the field of physical security alarm systems, where sensor switches in intrusion alarm circuits include roller-tipped plungers to be depressed by a moving body such as a door being closed.
For dependability many sensor switch assemblies included in intrusion alarm systems incorporate magnetically actuated reed contacts. For example, Holce U.S. Pat. No. 4,456,897 discloses a plunger-operated switch assembly including a magnetic reed contact. Holce et al. U.S. Pat. No. 4,336,518 discloses a switch assembly including a roller which moves a sliding plunger carrying a magnet which actuates a magnetic reed contact. The magnet used in such plunger switch assemblies in the past has typically been a small bar magnet carried in the plunger and having an axis of polarity aligned in the direction of reciprocal movement of the plunger, in order to achieve a reliable actuation of the reed switch at a desired position of the plunger. The arrangement of parts within such switch assemblies has resulted, however, in switch assemblies typically having a length of at least 1 1/2 inches. The housing of such a switch assembly must be long enough to contain a roller, a plunger, a plunger spring, and an encapsulated magnetic reed contact located where a magnet carried in the plunger can move far enough along the reed switch capsule to operate the magnetic reed contact. In some such switch assemblies separate parts of a housing must be glued, welded, or otherwise fastened together contributing to a significant labor item in the cost of manufacture.
A disadvantage of such previously available plunger switch assemblies is that a cavity deep enough to receive the switch assembly must be provided, in order to mount the switch assembly unobtrusively for use as part of an intrusion detection sensor circuit. It is desirable to be able to fit the switch assembly entirely within the frame surrounding a doorway or window opening, because in some cases it may be difficult to form a cavity to receive the switch assembly in structural materials surrounding a doorway or window frame. The larger the cavity which must be formed to receive such a switch assembly, the longer it usually takes to make such a cavity. As a result, if a smaller cavity is required less time is required for installation of such a switch assembly, and a security system sensor circuit can be installed more quickly and less expensively. It is therefore desired to have a plunger-operated switch assembly which is compact enough to be mounted flush within a small cavity, yet which has the reliability available from magnetically actuated reed switches.
Manufacture of some previously available switch assemblies incorporating magnetic reed contacts has required installation of the magnetic reed contacts in a housing in a particular orientation, as well as requiring adjustment of the position of a biasing magnet, helper magnet, or actuating magnet, either during assembly or during installation of such a switch assembly. Such orientation or adjustment steps also require a certain amount of time and thereby increase the cost of manufacture or installation of such switch assemblies.
It is therefore desired to provide an inexpensive switch assembly with a roller plunger, which has the reliability of a magnetic reed contact, which is contained in a housing small enough to be installed in a small cavity, and which can be manufactured using readily available inexpensive magnetic reed contacts and actuating magnets and without requiring separate steps to orient and adjust the location of magnetic reed contacts, biasing magnets or helper magnets.